The contribution of the lungs to thoracic impedance measurements: a simulation study based on a high resolution finite difference model.

A high resolution electrical finite difference model of the human thorax based on a 43 slice MRI data set along with lead field theory was used to examine the contribution of the lungs to the total impedance for a typical mid-thoracic 2D EIT eight and sixteen electrode configuration. Regional analysis of the thoracic sources of impedance revealed that the maximum contribution of lungs to the total impedance was approximately 22% for the eight electrode array and 25% for the sixteen electrode array. Analysis of impedance distribution of the lungs using a mid-thoracic application showed that the contribution of impedance of each slice followed closely the volume of the lungs in the given slice. This suggests that the mid-thoracic application gives results reflecting the entire lung. The contributions of the lung impedance for the various electrode positions showed that the eight electrode configuration had a more smooth change between adjacent electrodes compared to the 16 electrode arrangement.